Reducing antenna multipath and Rayleigh fading

ABSTRACT

Systems, methods, and apparatus for reducing antenna multipath and Rayleigh fading are disclosed. In one or more embodiments, a disclosed method for reducing multipath and Rayleigh fading for an antenna comprises receiving, by a structure, at least one undesired electromagnetic (EM) signal. In one or more embodiments, the structure is mounted proximate the antenna. In at least one embodiment, the structure comprises absorber material and/or reflective material. In one or more embodiments, the antenna is mounted on top of the structure. In at least one embodiment, the structure further comprises a core, where the core is covered by the absorber material and/or the reflective material. In at least one embodiment, the core is in the shape of a sphere, a hemisphere, at least a portion of a sphere, an ellipsoid, a torus, a pyramid, a cube, a cuboid, a cylinder, a cone, a polyhedron, or a freeform shape.

FIELD

The present disclosure relates to antenna multipath and Rayleigh fading.In particular, it relates to reducing antenna multipath and Rayleighfading.

BACKGROUND

Receive antennas, both terrestrial and in space, commonly experiencemultipath and Rayleigh fading. Multipath is a propagation phenomenonthat results from undesired signals reaching a receive antenna by two ormore paths. Causes of multipath include, but are not limited to,atmospheric ducting, ionospheric reflection and refraction, andreflection from bodies of water and objects, such as buildings,mountains, structures, and the ground. Multipath causes multipathinterference (including constructive and destructive interference) andphase shifting of the desired signal. Destructive interference, inparticular, causes signal fading, where magnitudes of the undesiredsignals have a distribution known as a Rayleigh distribution, which iscommonly referred to as Rayleigh fading.

Currently, to combat multipath and Rayleigh fading, expensive andcomplicated solutions are implemented, such as diversity techniques,channel coding, and equalization techniques. There is therefore a needfor an improved technique for reducing antenna multipath and Rayleighfading that is cost effective and easy to implement.

SUMMARY

The present disclosure relates to a method, system, and apparatus forreducing antenna multipath and Rayleigh fading. In one or moreembodiments, a method for reducing multipath and Rayleigh fadingcomprises receiving, by a structure, at least one undesiredelectromagnetic (EM) signal. In one or more embodiments, the structureis mounted proximate the antenna. In at least one embodiment, thestructure comprises absorber material and/or reflective material.

In one or more embodiments, the antenna is airborne, terrestrial, ormarine. In some embodiments, the antenna is a receive antenna, or atransmit and receive antenna.

In at least one embodiment, the antenna is mounted on top of thestructure. In some embodiments, at least a portion of the structuresurrounds at least a portion of the antenna.

In one or more embodiments, the structure further comprises a core,where the core is covered by the absorber material and/or the reflectivematerial. In some embodiments, the core comprises a shape of a sphere, ahemisphere, at least a portion of a sphere, an ellipsoid, a torus, apyramid, a cube, a cuboid, a cylinder, a cone, a polyhedron, and/or afreeform shape.

In at least one embodiment, the absorber material comprises carbon,metal, metal particles, polypyrrole, and/or polyaniline. In someembodiments, the absorber material comprises pyramidal absorber, taperedloading absorber, and/or matching layer absorber. In at least oneembodiment, the absorber material absorbs radio frequency (RF) signals.

In one or more embodiments, the structure is mounted on a vehicle. In atleast one embodiment, the vehicle is an airborne vehicle, a terrestrialvehicle, or a marine vehicle.

In at least one embodiment, a system for reducing multipath and Rayleighfading for an antenna comprises the antenna and a structure to receiveat least one undesired electromagnetic (EM) signal. In one or moreembodiments, the structure is mounted proximate the antenna. In at leastone embodiment, the structure comprises absorber material and/orreflective material.

The features, functions, and advantages can be achieved independently invarious embodiments of the present disclosure or may be combined in yetother embodiments.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a diagram showing an exemplary antenna experiencing multipath.

FIG. 2A is a diagram showing the disclosed system for reducing multipathand Rayleigh fading for an antenna that employs an antenna, which ismounted on a structure in the shape of a sphere that is mounted on apole stand, receiving signals from a satellite, in accordance with atleast one embodiment of the present disclosure.

FIG. 2B is a diagram showing the disclosed system for reducing multipathand Rayleigh fading for an antenna that employs an antenna, which ismounted on a structure in the shape of a sphere, receiving signals froma cellular tower, in accordance with at least one embodiment of thepresent disclosure.

FIG. 2C is a diagram showing a cross-sectional view of an exemplarystructure employed by the disclosed system for reducing multipath andRayleigh fading for an antenna that employs an antenna, in accordancewith at least one embodiment of the present disclosure.

FIG. 3A-3L are diagrams showing various different shapes that may beemployed for the structure of the disclosed system for reducingmultipath and Rayleigh fading for an antenna, in accordance with atleast one embodiment of the present disclosure.

FIG. 3A is a diagram showing a structure in the shape of a sphere, inaccordance with at least one embodiment of the present disclosure.

FIG. 3B is a diagram showing a structure in the shape of an ellipsoid,in accordance with at least one embodiment of the present disclosure.

FIG. 3C is a diagram showing a structure in shape comprising anellipsoid on a freeform shape, in accordance with at least oneembodiment of the present disclosure.

FIG. 3D is a diagram showing a structure in the shape of a four-sidedpyramid, in accordance with at least one embodiment of the presentdisclosure.

FIG. 3E is a diagram showing a structure in a shape comprising a cuboidon a torus, in accordance with at least one embodiment of the presentdisclosure.

FIG. 3F is a diagram showing a structure comprising a three-dimensional(3D) freeform shape, in accordance with at least one embodiment of thepresent disclosure.

FIG. 3G is a diagram showing a structure in the shape of a polyhedron,in accordance with at least one embodiment of the present disclosure.

FIG. 3H is a diagram showing a structure in the shape of a hemisphere,in accordance with at least one embodiment of the present disclosure.

FIG. 3I is a diagram showing a structure in the shape of a three-sidedpyramid, in accordance with at least one embodiment of the presentdisclosure.

FIG. 3J is a diagram showing a structure in the shape of a 3D diamond,in accordance with at least one embodiment of the present disclosure.

FIG. 3K is a diagram showing a structure in a shape comprising ahemisphere on a sphere, in accordance with at least one embodiment ofthe present disclosure.

FIG. 3L is a diagram showing a structure in a shape comprising ahemisphere on a cuboid, in accordance with at least one embodiment ofthe present disclosure.

FIGS. 4A-4C are diagrams showing a various different shapes that may beutilized for the structure of the disclosed system for reducingmultipath and Rayleigh fading for an antenna, where the structure ismounted on a pole stand, in accordance with at least one embodiment ofthe present disclosure.

FIG. 4A is a diagram showing a structure in the shape of a 3D diamondmounted on a pole stand, in accordance with at least one embodiment ofthe present disclosure.

FIG. 4B is a diagram showing a structure in the shape of a pyramidmounted on a pole stand, in accordance with at least one embodiment ofthe present disclosure.

FIG. 4C is a diagram showing a structure in the shape of a polyhedronmounted on a pole stand, in accordance with at least one embodiment ofthe present disclosure.

FIGS. 5A and 5B are diagrams showing structures mounted on differenttypes of vehicles that may be employed for the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure.

FIG. 5A is a diagram showing a structure in the shape of a hemispheremounted on a car, in accordance with at least one embodiment of thepresent disclosure.

FIG. 5B is a diagram showing multiple structures that are each in theshape of a hemisphere and mounted on an airplane, in accordance with atleast one embodiment of the present disclosure.

FIGS. 6A-6C are diagrams showing various different types of absorbermaterials that may be employed for the material of the structure of thedisclosed system for reducing multipath and Rayleigh fading for anantenna, in accordance with at least one embodiment of the presentdisclosure.

FIG. 6A is a diagram showing a side view of exemplary pyramidal absorbermaterial that may be employed for the structure of the disclosed systemfor reducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure.

FIG. 6B is a diagram showing a side view of exemplary tapered loadingabsorber material that may be employed for the structure of thedisclosed system for reducing multipath and Rayleigh fading for anantenna, in accordance with at least one embodiment of the presentdisclosure.

FIG. 6C is a diagram showing a side view of exemplary matched absorbermaterial that may be employed for the structure of the disclosed systemfor reducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure.

FIG. 7A is a diagram showing a perspective view of exemplary pyramidalabsorber material that may be employed for the structure of thedisclosed system for reducing multipath and Rayleigh fading for anantenna, in accordance with at least one embodiment of the presentdisclosure.

FIG. 7B is a diagram showing an overhead view of exemplary pyramidalabsorber material that may be employed for the structure of thedisclosed system for reducing multipath and Rayleigh fading for anantenna, in accordance with at least one embodiment of the presentdisclosure.

FIGS. 8A-8I are diagrams showing various different types of antennasthat may be employed for the antenna of the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure.

FIG. 8A is a diagram showing an exemplary dipole antenna that may beemployed for the antenna for the disclosed system for reducing multipathand Rayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure.

FIG. 8B is a diagram showing an exemplary bowtie antenna that may beemployed for the antenna for the disclosed system for reducing multipathand Rayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure.

FIG. 8C is a diagram showing an exemplary monopole antenna that may beemployed for the antenna for the disclosed system for reducing multipathand Rayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure.

FIG. 8D is a diagram showing an exemplary inductor loaded monopoleantenna that may be employed for the antenna for the disclosed systemfor reducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure.

FIG. 8E is a diagram showing an exemplary pyramidal horn antenna thatmay be employed for the antenna for the disclosed system for reducingmultipath and Rayleigh fading for an antenna, in accordance with atleast one embodiment of the present disclosure.

FIG. 8F is a diagram showing an exemplary tower antenna that may beemployed for the antenna for the disclosed system for reducing multipathand Rayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure.

FIG. 8G is a diagram showing an exemplary parabolic reflector antennathat may be employed for the antenna for the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure.

FIG. 8H is a diagram showing an exemplary omni-directional antenna thatmay be employed for the antenna for the disclosed system for reducingmultipath and Rayleigh fading for an antenna, in accordance with atleast one embodiment of the present disclosure.

FIG. 8I is a diagram showing an exemplary Yagi-Uda antenna that may beemployed for the antenna for the disclosed system for reducing multipathand Rayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure.

DESCRIPTION

The methods and apparatus disclosed herein provide an operative systemfor reducing antenna multipath and Rayleigh fading. The disclosed systememploys a structure, comprising radio frequency (RF) absorber materialand/or reflective material, mounted proximate to a receive antenna toabsorb and/or reflect any undesired RF signals. The structure is shapedand mounted proximate the antenna such that at least a portion of thesurface of the structure is normal to incoming undesired multipathsignals. This causes the undesired multipath signals to be attenuatedwithin the absorber material with any remaining signals reflected backtowards the source of the signals and not the receiving antenna, and/orto be reflected back to the source by the reflective material.

As previously mentioned above, receive antennas, both terrestrial and inspace, commonly experience multipath and Rayleigh fading. Multipath is apropagation phenomenon that results from undesired signals reaching areceiving antenna by two or more paths. Causes of multipath may includeatmospheric ducting, ionospheric reflection and refraction, andreflection from bodies of water and objects, such as buildings,mountains, structures, and the ground. Multipath causes multipathinterference (including constructive and destructive interference) andphase shifting of the desired signal. Destructive interference, inparticular, causes signal fading, where magnitudes of the undesiredsignals have a distribution known as a Rayleigh distribution, referredto as Rayleigh fading. Currently, to combat multipath and Rayleighfading, expensive and complicated solutions are implemented, such asdiversity techniques (e.g., antenna diversity by utilizing multipleantennas, spatial diversity amongst antennas, antenna polarizationdiversity, frequency diversity, and time diversity), channel coding(e.g., to correct for multipath), and equalization techniques (e.g., tocombat intersymbol interference (ISI) created by multipath).

The disclosed system employs a structure that comprises the combinationof a uniquely shaped core covered with RF absorber material and/orreflective material that can be applied to satellite and/or groundsystems to solve the widely-experienced communication channel problem ofmultipath and Rayleigh fading. The disclosed structure can be applied toany receive antenna and any communication system to reduce and minimizemultipath and Rayleigh fading. In particular, for the disclosedstructure, RF absorber material and/or reflective material is mounted ona shaped surface (e.g., a core) such that at least a portion of thesurface of the structure is normal to the incoming undesired signals.This allows for undesired multipath signals to be attenuated within theabsorber material with any small remaining signals to be reflected backtowards the source and not the receiving antenna, and/or reflected backto the source by the reflective material. The covered surface is shapedto be normal to the incoming undesired multipath signals and is locatedin the nearby vicinity of the receive antenna. The shape can bespherical or any other geometrical shape based on the surface of thestructure being perpendicular/normal to the incoming undesired RFsignals. In one or more embodiments, the structure is placed below andaround the receive antenna, where the significant small-scale multipathsignals are prevalent.

The surface of the absorber material and/or the reflective material isshaped to be at normal incidence to the incoming undesired multipathsignals to minimize multipath. This is because the attenuation and/orreflection of the RF signals is maximized for high angles of incidence(i.e. when the angle of incidence of the incoming wave is perpendicularor normal to the RF absorbing material, the absorption is maximized andthe reflection minimized; and when the angle of incidence of theincoming wave is perpendicular or normal to the reflective material, thereflection is maximized). As such, this lends itself to employing aspherical shape or hemispherical shape for the structure for satelliteand ground systems where the signals are visible from horizon tohorizon. The absorber material will attenuate the undesired multipathsignals until some small fraction of the incident waves will bereflected back from the absorber material, and any remaining reflectingsignals are reflected directly back towards the direction of the sourceso that the receiving antenna does not see any multipath interference.

In the following description, numerous details are set forth in order toprovide a more thorough description of the system. It will be apparent,however, to one skilled in the art, that the disclosed system may bepracticed without these specific details. In the other instances, wellknown features have not been described in detail so as not tounnecessarily obscure the system.

Embodiments of the present disclosure may be described herein in termsof functional and/or logical components and various processing steps. Itshould be appreciated that such components may be realized by any numberof hardware, software, and/or firmware components configured to performthe specified functions. For example, an embodiment of the presentdisclosure may employ various integrated circuit components (e.g.,memory elements, digital signal processing elements, logic elements,look-up tables, or the like), which may carry out a variety of functionsunder the control of one or more processors, microprocessors, or othercontrol devices. In addition, those skilled in the art will appreciatethat embodiments of the present disclosure may be practiced inconjunction with other components, and that the system described hereinis merely one example embodiment of the present disclosure.

For the sake of brevity, conventional techniques and components relatedto antenna systems, and other functional aspects of the system (and theindividual operating components of the systems) may not be described indetail herein. Furthermore, the connecting lines shown in the variousfigures contained herein are intended to represent example functionalrelationships and/or physical couplings between the various elements. Itshould be noted that many alternative or additional functionalrelationships or physical connections may be present in an embodiment ofthe present disclosure.

FIG. 1 is a diagram 100 showing an exemplary antenna 110 experiencingmultipath. In this figure, an antenna 110 is shown to be mounted on apole stand 150 that is standing on the ground 140. The antenna 110, inFIG. 1, is an omnidirectional antenna. However, it should be noted thatvarious different types of antennas may be employed for the antenna 110rather than an omnidirectional antenna as is shown in FIG. 1.

In particular, in FIG. 1, the antenna 110 is shown to be receiving adesired signal 120 that is transmitted from a source (not shown). Inaddition, the antenna 110 is shown to be experiencing multipath fromundesired signals 130. In this example of multipath, the undesiredsignals 130 are transmitted from the source (not shown), and arereflected off of the ground 140 prior to be received by the antenna 110.The undesired signals 130 can cause multipath interference, which caninclude constructive and destructive interference, and phase shifting ofthe desired signal 120.

FIG. 2A is a diagram 200 showing the disclosed system for reducingmultipath and Rayleigh fading for an antenna that employs an antenna210, which is mounted on a structure 240 in the shape of a sphere thatis mounted on a pole stand 250, receiving signals from a satellite 260,in accordance with at least one embodiment of the present disclosure. Inthis figure, the antenna 210 is shown to be mounted on top of thestructure 240 that is mounted on the pole stand 250, which is mounted orstanding on the ground. In other embodiments, the structure 240 may bemounted directly on the ground, on a building, or on a vehicle. FIGS. 5Aand 5B, for example, show structures mounted on different types ofvehicles that may be employed for the disclosed system. It should benoted that, in one or more embodiments, the structure 240 and antenna210 are mounted in an outside environment (i.e. not in a test chamber).

In FIG. 2A, the antenna 210 is a receive antenna. Alternatively, theantenna 210 may be a dual receive and transmit antenna. The antenna 210,in FIG. 2A, is an omnidirectional antenna. In other embodiments, variousdifferent types of antennas may be employed for the antenna 210 of thedisclosed system rather than an omnidirectional antenna as is shown inFIG. 2A. For example, FIGS. 8A-8I show some examples various differenttypes of antennas that may be employed for the antenna 210 of thedisclosed system.

The structure 240, in FIG. 2A, is in the shape of a sphere. However, inother embodiments of the disclosed system, the structure 240 may be inthe form of various different geometrical or freeform three-dimensional(3D) shapes. For example, FIGS. 3A-3L show some examples of variousdifferent shapes that may be employed for the structure 240 of thedisclosed system. The structure 240 comprises a core (refer to 295 ofFIG. 2C) covered by material (refer to 292 of FIG. 2C), which maycomprise absorber material and/or reflective material. It should benoted that, in some embodiments, the structure 240 may comprise absorbermaterial, may comprise reflective material, or may be a hybrid structurethat comprises both absorber material on some areas of the structure 240and reflective material on other areas of the structure 240. Theabsorber material is capable of absorbing electromagnetic (EM) signals,and particularly radio frequency (RF) signals; and the reflectivematerial is capable of reflecting electromagnetic (EM) signals, andparticularly radio frequency (RF) signals.

In FIG. 2A, the antenna 210 is shown to be receiving a desired signal220 that is transmitted from a source 260. The source 260, in FIG. 2A,is shown to be a satellite. However, in other embodiments, variousdifferent types of sources may be utilized for the source 260 including,but not limited to, ground antennas (e.g., ground stations or cellulartowers) or antennas mounted on vehicles (e.g., airborne vehicles,terrestrial vehicles, or marine vehicles). In addition, an undesiredsignal 230 is shown to have originated from the source 260. If thestructure 240 employs absorber material, the absorber material of thestructure 240 receives and absorbs the undesired signal 230 so that theantenna 210 does not experience multipath. And, if the structure 240employs reflective material, the reflective material of the structure240 reflects the undesired signal 230 away from the antenna 210 (ideallyreflects the undesired signal 230 back towards the source 260) so thatthe antenna 210 does not experience multipath.

The shape of the structure 240, as well as the mounting position of theantenna 210 in relation to the structure 240, is chosen such that thesurface of the structure 240 is (as much as possible) at normalincidence to incoming undesired signals 230. This helps to minimize themultipath experienced by the antenna 210 because the attenuation and/orreflection of the undesired signals 230 is maximized for high angles ofincidence (i.e. when the angle of incidence of the incoming wave isperpendicular or normal to the surface of the absorber material, theabsorption of the undesired signals 230 is maximized and the reflectionis minimized; and when the angle of incidence of the incoming wave isperpendicular or normal to the surface of the reflective material, thereflection of the undesired signals 230 is maximized).

FIG. 2B is a diagram 270 showing the disclosed system for reducingmultipath and Rayleigh fading for an antenna that employs an antenna280, which is mounted on a structure 285 in the shape of a sphere,receiving signals from a cellular tower 275, in accordance with at leastone embodiment of the present disclosure. This figure shows a monopoleantenna 280 mounted on a structure 285 in the shape of a sphere. Theantenna 280 is shown to be receiving a desired signal 278 transmittedfrom a source 275, which is a cellular tower. The structure 285comprises a core (refer to 295 of FIG. 2C) covered by material (refer to292 of FIG. 2C), which may comprise absorber material and/or reflectivematerial. If the structure 285 is employs absorber material, theabsorber material of the structure 285 receives and absorbs theundesired signal 277, which originated from the source 275, so that theantenna 280 does not experience multipath. And, if the structure 285 isemploys reflective material, the reflective material of the structure285 receives and reflects the undesired signal 277, which originatedfrom the source 275, so that the antenna 280 does not experiencemultipath.

FIG. 2C is a diagram 290 showing a cross-sectional view of an exemplarystructure 291 employed by the disclosed system for reducing multipathand Rayleigh fading for an antenna that employs an antenna, inaccordance with at least one embodiment of the present disclosure. Inthis figure, the structure 291 is in the shape of a sphere, and is shownto comprise a core 295 covered by material 292. The underside of thematerial 292 is bonded to the exterior surface of the core 295 by abond. It should be noted that the material 292 may comprise absorbermaterial and/or reflective material.

The core 295, in FIG. 2C, is in the shape of a sphere. However, in otherembodiments, the core 295 may be of various different three-dimensional(3D) geometrical or freeform shapes other than a sphere including, butnot limited to, a hemisphere, at least a portion of a sphere, anellipsoid, a torus, a three-sided pyramid, a four-sided pyramid, a cube,a cuboid, a cylinder, a cone, a polyhedron, a freeform shape, or acombination thereof. The core 295 may be manufactured from variousdifferent materials including, but not limited to, natural materials(e.g., wood and/or metals) and/or synthetic materials (e.g., plasticsand/or polymers).

If the material 292 comprises absorber material, the absorber materialis electromagnetic (EM) absorber material that absorbs EM radiation. Inone or more embodiments, the absorber material is radio frequency (RF)absorber material that absorbs RF signals. The absorber material may bemanufactured from various different materials including, but not limitedto, carbon (e.g., coating mats of animal hair mixed with carbon black),metal (e.g., iron oxide), metal particles (aluminum metal particlesand/or powered iron), polypyrrole (which may be employed with latex,polymer blends, and/or fibers), polyaniline (i.e. a conducting polymer),and a combination thereof. In addition, various different forms ofabsorber material may be utilized for the material 292 including, butnot limited to, pyramidal absorber (refer to FIG. 6A), tapered loadingabsorber (FIG. 6B), and matching layer absorber (FIG. 6C).

If the material 292 comprises reflective material, the reflectivematerial reflects EM radiation. The reflective material may bemanufactured from various different materials including, but not limitedto, metals, graphite, composite materials, and a combination thereof.

FIG. 3A-3L are diagrams showing various different shapes that may beemployed for the structure of the disclosed system for reducingmultipath and Rayleigh fading for an antenna, in accordance with atleast one embodiment of the present disclosure. It should be noted thatthe different shapes shown in FIGS. 3A-3L are only some of the variousdifferent geometrical and freeform shapes that may be utilized for thestructure of the disclosed system. In one or more embodiments, thestructure of the disclosed system may be of various differentthree-dimensional (3D) geometrical or freeform shapes including, but notlimited to, a sphere, a hemisphere, at least a portion of a sphere, anellipsoid, a torus, a three-sided pyramid, a four-sided pyramid, a cube,a cuboid, a cylinder, a cone, a polyhedron, a freeform shape, or acombination thereof. In addition, in this figures, it should be notedthat the antennas mounted on the various different structures are allmonopole antennas. However, in other embodiments of the disclosedsystem, various different types of antennas may be employed instead of amonopole antenna, as is depicted in these figures. For example, FIGS.8A-8I show some examples various different types of antennas that may beemployed for the disclosed system. Additionally, it should be noted thatthe antenna may be mounted on the structure such that at least a portionof the structure surrounds at least a portion of the antenna.

FIG. 3A is a diagram showing a structure 302 in the shape of a sphere,in accordance with at least one embodiment of the present disclosure. Inthis figure, a monopole antenna 301 is shown to be mounted on thespherical structure 302. FIG. 3B is a diagram showing a structure 304 inthe shape of an ellipsoid, in accordance with at least one embodiment ofthe present disclosure. In this figure, a monopole antenna 303 is shownto be mounted on the structure 304, which is an ellipsoid. FIG. 3C is adiagram showing a structure 306 in shape comprising an ellipsoid 307 ona freeform shape 308, in accordance with at least one embodiment of thepresent disclosure. A monopole antenna 305 is shown to be mounted on theellipsoid 307 portion of the structure 306 of FIG. 3C. FIG. 3D is adiagram showing a structure 310 in the shape of a four-sided pyramid, inaccordance with at least one embodiment of the present disclosure. Inthis figure, a monopole antenna 309 is shown to be mounted on thepyramidal structure 310.

FIG. 3E is a diagram showing a structure 312 in a shape comprising acuboid 314 on a torus 313, in accordance with at least one embodiment ofthe present disclosure. A monopole antenna 311 is shown to be mounted onthe cuboid 314 portion of the structure 312. FIG. 3F is a diagramshowing a structure 316 comprising a three-dimensional (3D) freeformshape, in accordance with at least one embodiment of the presentdisclosure. In this figure, two monopole antennas 315 a, 315 b are shownto be mounted at two different locations on peaks of the freeformstructure 316.

FIG. 3G is a diagram showing a structure 318 in the shape of apolyhedron, in accordance with at least one embodiment of the presentdisclosure. In this figure, a monopole antenna 317 is shown to bemounted on the structure 318, which is a polyhedron. It should be notedthat in other embodiments of the disclosed system, the structure 318 maybe in the shape of various different polyhedrons comprising more or lesssides than the polyhedron depicted in FIG. 3G. FIG. 3H is a diagramshowing a structure 320 in the shape of a hemisphere, in accordance withat least one embodiment of the present disclosure. A monopole antenna319 is shown to be mounted on the hemispherical structure 320. It shouldbe noted that in some embodiments of the disclosed system, the structure320 may be in the shape of a portion of a sphere that may comprise lessthan or more than a hemisphere, as is shown in FIG. 3H.

FIG. 3I is a diagram showing a structure 322 in the shape of athree-sided pyramid, in accordance with at least one embodiment of thepresent disclosure. In this figure, a monopole antenna 321 is shown tobe mounted on the pyramidal structure 322. FIG. 3J is a diagram showinga structure 324 in the shape of a 3D diamond, in accordance with atleast one embodiment of the present disclosure. In this figure, themonopole antenna 323 is shown to be mounted on a peak of thediamond-shaped structure 324.

FIG. 3K is a diagram showing a structure 326 in a shape comprising ahemisphere 327 on a sphere 328, in accordance with at least oneembodiment of the present disclosure. A monopole antenna 325 is shown tobe mounted on the hemisphere 327 portion of the structure 326. FIG. 3Lis a diagram showing a structure 330 in a shape comprising a hemisphere331 on a cuboid 332, in accordance with at least one embodiment of thepresent disclosure. In this figure, a monopole antenna 329 is shown tobe mounted on the hemisphere 331 portion of the structure 330.

FIGS. 4A-4C are diagrams showing a various different shapes that may beutilized for the structure of the disclosed system for reducingmultipath and Rayleigh fading for an antenna, where the structure ismounted on a pole stand, in accordance with at least one embodiment ofthe present disclosure. It should be noted that, in one or moreembodiments, the pole of the pole stand may be manufactured from variousdifferent materials including, but not limited to, natural materials(e.g., wood and/or metals) and/or synthetic materials (e.g., plasticsand/or polymers). In addition, the structures mounted pole stands may beof various different geometric and freeform shapes other than the fewshapes depicted in these figures, and the antennas mounted on thestructure may be of various different types of antennas than themonopole antenna shown in these figures.

FIG. 4A is a diagram showing a structure 402 in the shape of a 3Ddiamond mounted on a pole stand 403, in accordance with at least oneembodiment of the present disclosure. In this figure, the monopoleantenna 401 is shown to be mounted on a peak of the diamond-shapedstructure 402. FIG. 4B is a diagram showing a structure 405 in the shapeof a pyramid mounted on a pole stand 406, in accordance with at leastone embodiment of the present disclosure. A monopole antenna is shown tobe mounted on the pyramidal structure 405. FIG. 4C is a diagram showinga structure 408 in the shape of a polyhedron mounted on a pole stand409, in accordance with at least one embodiment of the presentdisclosure.

FIGS. 5A and 5B are diagrams showing structures mounted on differenttypes of vehicles that may be employed for the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. It should benoted that for the disclosed system, the structures may be mounted onvarious different types of vehicles including, but not limited to,terrestrial vehicles (e.g., cars, trucks, and tanks) where theassociated antenna is a terrestrial antenna, airborne vehicles (e.g.,airplanes, aircraft, and satellites) where the associated antenna is anairborne antenna, and marine vehicles (e.g., ships and boats) where theassociated antenna is a marine antenna. In addition, it should be notedthat, in some embodiments, the shape of the structure to be mounted onthe vehicle is chosen such that the structure is aerodynamic.

Also, it should be noted that in FIGS. 5A and 5B, the size of thestructures in relation to the vehicles is for illustration purposes andcan vary widely. As such, the disclosed system may employ structuresthat are larger or smaller than the structures depicted in FIGS. 5A and5B in relation to the size of the illustrated vehicles. For example, thedisclosed system may employ structures that are smaller in size than thestructures shown in these figures in relation to the size of thevehicles so that the structures may be more aerodynamic (e.g., small lowdrag structures).

FIG. 5A is a diagram 500 showing a structure 510 in the shape of ahemisphere mounted on a car 545, in accordance with at least oneembodiment of the present disclosure. In this figure, the structure 510is mounted on the exterior of the roof of the car 545. The antenna 520is shown to be mounted on top of a structure 510. The antenna 520, inFIG. 5A, is an omnidirectional antenna. In other embodiments, variousdifferent types of antennas may be employed for the antenna 520 of thedisclosed system rather than an omnidirectional antenna as is shown inFIG. 5A. The structure 510, in FIG. 5A, is in the shape of a hemisphere.However, in other embodiments of the disclosed system, the structure 240may be in the form of various different geometrical or freeformthree-dimensional (3D) shapes.

In FIG. 5A, the antenna 520 is shown to be receiving a desired signal530 that is transmitted from a source (not shown). In addition,undesired signals 540 are shown, which have originated from the source(not shown). The absorber material of the structure 510 receives andabsorbs the undesired signals 540 so that the antenna 520 does notexperience multipath.

FIG. 5B is a diagram showing multiple structures 560 a, 560 b, 560 cthat are each in the shape of a hemisphere and mounted on an airplane580, in accordance with at least one embodiment of the presentdisclosure. In this figure, the structures 560 a, 560 b, 560 c aremounted at various different locations on the exterior of the airplane580. A monopole antenna 570 a, 570 b, 570 c is mounted on each of thestructures 560 a, 560 b, 560 c, respectively.

FIGS. 6A-6C are diagrams showing various different types of absorbermaterials that may be employed for the material of the structure of thedisclosed system for reducing multipath and Rayleigh fading for anantenna, in accordance with at least one embodiment of the presentdisclosure. It should be noted that various different types of absorbermaterial may be employed for the disclosed structure other than the fewvarious different types of absorber material that are shown in thesefigures.

FIG. 6A is a diagram showing a side view of exemplary pyramidal absorbermaterial that may be employed for the structure of the disclosed systemfor reducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. Pyramidalabsorber provides a gradual impedance transition from air to theabsorber. The shape of pyramidal absorber is a cone-like structure (e.g.refer to FIG. 7A), which is arranged perpendicular to the surface thatthe pyramidal absorber is bonded (refer to FIG. 7B). The height andperiodicity of the pyramidal absorber may be about one wavelength long.

FIG. 6B is a diagram showing a side view of exemplary tapered loadingabsorber material that may be employed for the structure of thedisclosed system for reducing multipath and Rayleigh fading for anantenna, in accordance with at least one embodiment of the presentdisclosure. Tapered loading absorber has a varied impedance (Z) gradingover one or more wavelengths. Tapered loading absorber is advantageousover pyramidal absorber due to its depth being thin in size. A thindepth of absorber material offers poor performance and, as such, withthe tapered loading absorber, the impedance gradient is varied over oneor more wavelengths to improve its performance. The tapered loadingabsorber is made from a combination of low loss and lossy materials. Thelossy material is dispersed parallel to the surface of the absorbermaterial with its gradient perpendicular to the surface, which increasesinto the body of the material.

FIG. 6C is a diagram showing a side view of exemplary matched absorbermaterial that may be employed for the structure of the disclosed systemfor reducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. Matched absorbermaterial has a thickness (d2) that is thinner than pyramidal absorbermaterial and tapered loading absorber material. Matched absorbermaterial employs an additional matching layer that lies in between airand the absorbing layer. The impedance of this transition layer isbetween the impedance of air (Z1) and the impedance of the absorbinglayer (Z2), where Z2=(Z1*Z3)*0.5.

FIG. 7A is a diagram 700 showing a perspective view of exemplarypyramidal absorber material 720 that may be employed for the structureof the disclosed system for reducing multipath and Rayleigh fading foran antenna, in accordance with at least one embodiment of the presentdisclosure. And, FIG. 7B is a diagram 710 showing an overhead view ofexemplary pyramidal absorber material 720 that may be employed for thestructure of the disclosed system for reducing multipath and Rayleighfading for an antenna, in accordance with at least one embodiment of thepresent disclosure.

FIGS. 8A-8I are diagrams showing various different types of antennasthat may be employed for the antenna of the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. It should benoted that various different types of antennas may be employed for thedisclosed system other than the few various different types of antennasthat are shown in these figures.

FIG. 8A is a diagram showing an exemplary dipole antenna 810 that may beemployed for the antenna for the disclosed system for reducing multipathand Rayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure. FIG. 8B is a diagram showing anexemplary bowtie antenna 820 that may be employed for the antenna forthe disclosed system for reducing multipath and Rayleigh fading for anantenna, in accordance with at least one embodiment of the presentdisclosure. FIG. 8C is a diagram showing an exemplary monopole antenna830 that may be employed for the antenna for the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. FIG. 8D is adiagram showing an exemplary inductor loaded monopole antenna 840 thatmay be employed for the antenna for the disclosed system for reducingmultipath and Rayleigh fading for an antenna, in accordance with atleast one embodiment of the present disclosure.

FIG. 8E is a diagram showing an exemplary pyramidal horn antenna 850that may be employed for the antenna for the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. It should benoted that in some embodiments, different types of horn antennas may beemployed by the disclosed system other than a pyramidal horn antennaincluding, but not limited to, a ring-loaded horn antenna, a step hornantenna, and a trifurcated horn antenna.

FIG. 8F is a diagram showing an exemplary tower antenna 860 that may beemployed for the antenna for the disclosed system for reducing multipathand Rayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure.

FIG. 8G is a diagram showing an exemplary parabolic reflector antenna870 that may be employed for the antenna for the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. In someembodiments, different types of reflector antennas may be employed bythe disclosed system other than a parabolic reflector antenna including,but not limited to, a shaped reflector antenna and a dual reflectorsystem (e.g., Cassagrain dual reflector system or Gregorian dualreflector system).

FIG. 8H is a diagram showing an exemplary omni-directional antenna 880that may be employed for the antenna for the disclosed system forreducing multipath and Rayleigh fading for an antenna, in accordancewith at least one embodiment of the present disclosure. FIG. 8I is adiagram showing an exemplary Yagi-Uda antenna 890 that may be employedfor the antenna for the disclosed system for reducing multipath andRayleigh fading for an antenna, in accordance with at least oneembodiment of the present disclosure.

Although particular embodiments have been shown and described, it shouldbe understood that the above discussion is not intended to limit thescope of these embodiments. While embodiments and variations of the manyaspects of the invention have been disclosed and described herein, suchdisclosure is provided for purposes of explanation and illustrationonly. Thus, various changes and modifications may be made withoutdeparting from the scope of the claims.

Where methods described above indicate certain events occurring incertain order, those of ordinary skill in the art having the benefit ofthis disclosure would recognize that the ordering may be modified andthat such modifications are in accordance with the variations of thepresent disclosure. Additionally, parts of methods may be performedconcurrently in a parallel process when possible, as well as performedsequentially. In addition, more parts or less part of the methods may beperformed.

Accordingly, embodiments are intended to exemplify alternatives,modifications, and equivalents that may fall within the scope of theclaims.

Although certain illustrative embodiments and methods have beendisclosed herein, it can be apparent from the foregoing disclosure tothose skilled in the art that variations and modifications of suchembodiments and methods can be made without departing from the truespirit and scope of the art disclosed. Many other examples of the artdisclosed exist, each differing from others in matters of detail only.Accordingly, it is intended that the art disclosed shall be limited onlyto the extent required by the appended claims and the rules andprinciples of applicable law.

I claim:
 1. A method that reduces multipath and Rayleigh fading for anantenna, the method comprising: receiving, by a structure, at least oneundesired electromagnetic (EM) signal, which is the multipath; and atleast one of absorbing or reflecting, by the structure, the multipath,wherein the structure is mounted on a vehicle and proximate the antenna,and the structure comprises a core covered by at least one of absorbermaterial or reflective material, and wherein the absorber material is anEM absorber material that absorbs EM radiation, and the reflectivematerial is an EM reflective material that reflects the EM radiation. 2.The method of claim 1, wherein the antenna is one of airborne,terrestrial, or marine.
 3. The method of claim 1, wherein the antenna isone of a receive antenna or a transmit and receive antenna.
 4. Themethod of claim 1, wherein the antenna is mounted on top of thestructure.
 5. The method of claim 1, wherein at least a portion of thestructure surrounds at least a portion of the antenna.
 6. The method ofclaim 1, wherein the core comprises a shape of one of a sphere, ahemisphere, at least a portion of a sphere, a pyramid, a cube, a cuboid,a cylinder, a cone, an ellipsoid, a torus, a polyhedron, a freeformshape, or a combination thereof.
 7. The method of claim 1, wherein theabsorber material comprises at least one of carbon, metal, metalparticles, polypyrrole, or polyaniline.
 8. The method of claim 1,wherein the absorber material comprises at least one of pyramidalabsorber, tapered loading absorber, or impedance matching layerabsorber.
 9. The method of claim 1, wherein the absorber materialabsorbs radio frequency (RF) signals.
 10. The method of claim 1, whereinthe vehicle is one of an airborne vehicle, a terrestrial vehicle, or amarine vehicle.
 11. The method of claim 1, wherein the structure ismounted proximate the antenna such that at least a portion of a surfaceof the structure is normal to incoming undesired multipath signals. 12.The method of claim 1, wherein the structure is shaped such that atleast a portion of a surface of the structure is normal to incomingundesired multipath signals.
 13. A system that reduces multipath andRayleigh fading for an antenna, the system comprising: the antenna; anda structure to receive at least one undesired electromagnetic (EM)signal, which is the multipath, and to at least one of absorb or reflectthe multipath, wherein the structure is mounted on a vehicle andproximate the antenna, and the structure comprises a core covered by atleast one of absorber material or reflective material, and wherein theabsorber material is an EM absorber material that absorbs EM radiation,and the reflective material is an EM reflective material that reflectsthe EM radiation.
 14. The system of claim 13, wherein the antenna ismounted on top of the structure.
 15. The system of claim 13, wherein atleast a portion of the structure surrounds at least a portion of theantenna.
 16. The system of claim 13, wherein the core comprises a shapeof one of a sphere, a hemisphere, at least a portion of a sphere, apyramid, a cube, a cuboid, a cylinder, a cone, a polyhedron, a freeformshape, or a combination thereof.
 17. The system of claim 13, wherein theabsorber material comprises at least one of carbon, metal, metalparticles, polypyrrole, or polyaniline.
 18. The system of claim 13,wherein the absorber material comprises at least one of pyramidalabsorber, tapered loading absorber, or impedance matching layerabsorber.
 19. The system of claim 13, wherein the vehicle is one of anairborne vehicle, a terrestrial vehicle, or a marine vehicle.
 20. Asystem that reduces multipath and Rayleigh fading for an antenna, thesystem comprising: the antenna to receive at least one desiredelectromagnetic (EM) signal transmitted from a source, wherein theantenna is mounted on a structure, and at least a portion of thestructure surrounds at least a portion of the antenna; a vehicle; andthe structure, which is a shape of a three-dimensional (3D) geometricalshape and comprises a core covered by at least one of absorber materialor reflective material, is mounted on the vehicle to at least one ofabsorb with the absorber material or to reflect with the reflectivematerial at least one undesired EM signal transmitted, which is themultipath, from the source, and wherein the absorber material is an EMabsorber material that absorbs EM radiation, and the reflective materialis an EM reflective material that reflects the EM radiation.